Project Summary/Abstract The goal of the MODEL-AD consortia at UC Irvine is to generate improved mouse models of sporadic, late- onset Alzheimer?s disease (AD). Ideally, such mice will develop facets of human AD pathology including neuritic plaques, neurofibrillary tangles, and widespread cortical and hippocampal neurodegeneration in advanced age. In order to validate these models we are performing a host of tests including long-term potentitiation experiments, behavioral, transcriptomic and pathological profiling. As pointed out by the December 2018 external advisory board meeting synaptic loss (a key hallmark of AD and one that correlates best with cognitive decline) is currently not being investigated and was specifically requested as an endpoint to be determined. Traditionally, electron microscopy (EM) has been used to quantify synapse density/morphology but laborious sample preparation and stringent requirements in labelling of endogenous proteins precludes high-throughput analysis. On the other hand, fluorescence microscopy readily allows multiple protein species to be efficiently labelled and imaged in 3D. However, studying sub-synaptic structures is difficult because of the small size of synapses, which is near the diffraction-limited resolution of light microscopy. To determine synapse density/morphology in our AD models we request a supplement to perform superresolution imaging using Stochastic Optical Reconstruction Microscopy (STORM). This single molecule localization technique permits the position of proteins to be determined in 3D with nanometer precision and allows a large number of synapses in different brain regions to be imaged in a rapid manner facilitating systematic comparative analysis.